Better synonym handling in Solr

Read the Tea Leaves

Update: Download the plugin on Github.

It’s a pretty common scenario when working with a Solr-powered search engine: you have a list of synonyms, and you want user queries to match documents with synonymous terms. Sounds easy, right? Why shouldn’t queries for “dog” also match documents containing “hound” and “pooch”? Or even “Rover” and “canis familiaris”?

As it turns out, though, Solr doesn’t make synonym expansion as easy as you might like. And there are lots of good ways to shoot yourself in the foot.

The SynonymFilterFactory

Solr provides a cool-sounding SynonymFilterFactory, which can be a fed a simple text file containing comma-separated synonyms. You can even choose whether to expand your synonyms reciprocally or to specify a particular directionality.

For instance, you can make “dog,” “hound,” and “pooch” all expand to “dog | hound | pooch,” or you can specify that “dog” maps to “hound”…

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